Phase Formation Process Research Articles

Sintering, crystallization and foaming of La2O3·SrO·5B2O3 glass powders - effect of the holding temperature and the heating rate

The peculiarities of sinter-crystallization of La2O3·SrO·5B2O3 fine glass powder (below 1μm) are investigated and discussed. The sintering was studied by contactless optical dilatometry and porosity measurements. The crystallization process was evaluated by differential scanning calorimetry (DSC) and the crystalline phase formation was analyzed by X-ray diffraction (XRD). Finally the microstructures of the samples sintered at different temperatures were observed by field emission scanning electron microscope (FESEM).The specific aim of this study was to highlight the influence of sintering temperature and heating rate on the densification process and the final structure of glass-ceramic samples. It was shown that zero water adsorption and minimum closed porosity of ~3% were obtained at heating rate of 2°C/min and at about 1h holding at 690°C. The temperature increase accelerated intense foaming process that resulted in formation of total porosity of 35–45%. It was also demonstrated that the foaming depended on the heating rate: the higher the heating rate – the more intensive was the bloating. The observed foaming process was related to intensive crystallization and re-crystallization of La2O3·SrO·5B2O3 crystal phase. The phase formation processes entirely completed after 30–60min at 730–740°C with the formation of intriguing and unusual crystal structures.

Choline derivative ionic liquids-based aqueous two-phase systems: Phase diagrams and partition of purine alkaloids

Abstract Searching for environmentally friendly aqueous two-phase systems is imperative for the sustainable development of separation technologies. In this work, five kinds of environmentally benign choline derivative ionic liquids were synthesized and used for the formation of aqueous two-phase systems with K3PO4, K3C6H5O7 or K2CO3. In order to understand the phase formation processes of these aqueous two-phase systems and their possible application in extraction, phase diagrams and partition coefficients of purine alkaloids were determined at T = 298.2 K, and the effects of structure of the ionic liquids, nature of the purine alkaloids, composition and temperature of the systems on the partitioning behaviour of purine alkaloids were investigated systematically. It was shown that caffeine, theobromine and 2,6-amino purine could be extracted effectively into the ionic liquid-rich phase of the aqueous two-phase systems, and the partition coefficients were as high as 4.5–42 under the optimized conditions. The partitioning was found to decrease with the increase of the ratio of H2O weight fraction (in the ionic liquid-rich phase and in the salt-rich phase) and hydrophobicity of both the purine alkaloids and the ionic liquids, but not sensitive to the change of temperature.

Tailoring luminescent colour and life persistence of undoped CdSiO3

In this work, undoped CdSiO3 samples with different luminescence spectra and light persistence were obtained by controlling the parameters of sol–gel synthesis. The process of monoclinic phase formation was monitored through XRD and TG-DTA measurements, combined to microstructural characterization using FTIR and SEM. The optical energy bandgap (Eg) of CdSiO3 was estimated from Tauc equation and indicates the dependency of bandgap energy on the starting pH used for synthesis. Three main peaks could be identified from PL and XEOL spectra, at 590nm, 490nm and 406nm. Their relative intensities yielded overall distinct luminescence colours, such as indigo or red. The luminescent mechanisms of CdSiO3 related to an intrinsic defect (VCd) were further investigated to show its key role in the charge trapping that causes long lasting luminescence.

Quick Activation of Nanoporous Anatase TiO2 as High-Rate and Durable Anode Materials for Sodium-Ion Batteries.

To understand the slow capacity activation behavior of anatase TiO2 as a sodium-ion battery anode during cycling, a nanoporous configuration was designed and prepared. On the basis of the comprehension of the Na-ion storage mechanism, the behavior is demonstrated to be related with the gradual formation of amorphous phase resulting from the phase transition during discharge. In addition, the level of phase transition is determined by the discharge rates and cycle numbers, which strongly affects the electrochemical performance of anatase TiO2. Via a quick formation process of the amorphous phase in the initial cycles, the capacity activation is accelerated, and high initial capacity is achieved with no fading after 500 cycles. Particularly, anatase TiO2 displays surprisingly unique properties in the fast charge (even at 20 C, 6.7 A g-1) mode, delivering a 179 mA h g-1 charge capacity. This study is significant for the comprehensive understanding of the controversial sodium storage mechanisms and unclear special behaviors occurring in anatase TiO2, thus greatly contributing to better guidance on the computational studies and experiment technologies for further performance promotion.

The Influence of Cavitation Treatment on Nano Structuring of Alkali Aluminosilicate Binder for Intumescent Coatings

This paper covers the results of study of the influence of cavitation treatment on nanostructuring of the alkali aluminosilicate binder for intumescent coatings. The results of study suggested to establish optimal parameters of cavitation treatment. At pressure of 20...25 atm, temperature below 30 °С, time of treatment shorter than 10 min rheological properties tend to improve and phase formation processes to accelerate at normal curing temperatures which result in the enhancement of heat engineering and mechanical properties of the intumescent coatings.

Impact of a Ni2+-influx on formation, stability, solubility and crystal structures of the magnesia cement phases 3-1-8 and 5-1-8 at 25 °C

The impact of a Ni2+-influx on formation, stability, solubility and crystal structures of the 3-1-8 (3 Mg(OH)2·MgCl2·8H2O) and the 5-1-8(5 Mg(OH)2·MgCl2·8H2O) binder phases of the magnesia cement system was studied by adding MgO, the 5-1-8 and the 3-1-8 phase to Ni2+-bearing 4.0 molal MgCl2-solutions at 25°C and applying equilibration periods of more than 2 years (up to 800days). Nickel was observed to enter the crystal structure of the 5-1-8 phase, yielding solid solutions among this magnesium chloride hydroxide hydrate and its Ni-analog, whereas no incorporation of Ni2+ ions into the crystal structure of the 3-1-8 phase takes place. The presence of nickel in the access solution inhibits the transformation of the metastable 5-1-8 phase into the thermodynamically stable 3-1-8 phase and prolongs the duration of this process from a few days to more than 2 years. As the final product of the phase formation process a mixture of the 3-1-8 phase and the 2-1-4 Ni-phase (2 Ni(OH)2·NiCl2·4H2O) could be identified. Analyses of the resulting liquid phases confirmed that almost the complete amount of dissolved nickel was removed from the solution by the addition of MgO, the 5-1-8 or the 3-1-8 phase.

Structural aspects of the phase and texture formation processes in thin-layer Ni-W/TiN systems which are perspective for creating high-temperature superconductors of the second generation

Structural aspects of the phase and texture formation processes in thin-layer Ni-W/TiN systems which are perspective for creating high-temperature superconductors of the second generation

Electron-Beam Welding - Structural-Phase State and Microhardnes in the Weld Zone in a Submicrocrystalline Titanium Alloy Grade2

The paper presents the results of the X-ray diffraction analysis of structural-phase states in the weld zone of a titanium alloy Grade2 in micro-and submicrocrystalline states. It is established that the structural-phase state in the weld zone and in the heat-affected zone depends on the state of samples of the alloy Grade2 before welding. It is shown that formation process of metastable phases ω-Ti and α′′-Ti occurs in the submicrocrystalline state in the alloy Grade2 in the weld zone and in the heat-affected zone. Investigations of the features of the microhardness distribution in the weld zone in alloys Grade2 in micro-and submicrocrystalline states are carried out. Different character of microhardness distributions in the weld zone in the samples depending on the structural-phase state of welded plates made of alloy Grade2 is determined.

Self-propagating high-temperature synthesis of nanocomposite ceramics TaSi2-SiC with hierarchical structure and superior properties

This study focuses on the investigation of the combustion kinetics and mechanisms, as well as the phase and structure formation processes, during elemental self-propagating high temperature synthesis of ceramics in Ta-Si-C system.Thermodynamic and kinetic features of SHS are discussed. Thermodynamic calculations, time-resolved XRD and investigation of stopped combustion front suggest the following chemical reactions sequence in combustion wave for the Ta-Si-C system: Ta+Sisolid+C→TaC+Sisolid+C→TaC+SiC+Siliquid+C→TaC+TaSi2+Ta5Si3+SiC+Sisolid+C→TaSi2+SiC.Significant microstructure refinement occurs due to the formation of SiC within the TaC, Ta5Si3 and TaSi2 particles during the SHS. Combustion products consist of agglomerated SiC and TaSi2 particles with the size of individual grains equal to 15–50nm. Hot pressing of TaSi2-SiC powders at 1600°C produces the bulk nanocomposites with a relative density of 97%. In comparison to similar materials reported in the literature, bulk SHS composite TaSi2-30%SiC exhibits superior hardness (19.1GPa) as well as fracture toughness (6.7MPam1/2) and shows a great potential for application as a structural material and as a precursor for ion-plasma deposition of high-temperature tribological coatings.

Phase formation and magnetic property evolution processes of the hexaferrite with composition BaO⋅0.9Sc2O3⋅5.1Fe2O3

The phase formation and magnetic property evolution processes of the hexaferrite with composition BaO⋅0.9Sc2O3⋅5.1Fe2O3 have been investigated. Results show that when the calcination temperature is lower than 1000 °C, the spinel phase BaFe2O4 and M-type hexaferrite phase BaFe12O19 dominate. The M-type hexaferrite BaFe12−xScxO19 (0 < x ≤ 1.8) appears above 1050 °C and becomes a single phase BaFe10.2Sc1.8O19 above 1200 °C. A two-step decrease of both the coercivity and remanence ratio is observed above 1050 °C, which agrees well with the appearance of soft magnetic phase BaFe12−xScxO19 (0 < x ≤ 1.8). The saturation magnetization of the sample increases with calcination temperature until 1100 °C and then decreases. Raman spectra results show that the above magnetic property evolutions can be explained by a temperature dependent incorporation of Sc3+ into the lattice sites nearby the magnetic blocks’ interfaces. This weakens the local magnetic exchange interactions between Fe3+ and thus leads to a change in the magnetic structure.

Core–Shell Structure of Palladium Hydride Nanoparticles Revealed by Combined X-ray Absorption Spectroscopy and X-ray Diffraction

We report an in situ, temperature and H2 pressure-dependent, characterization of (2.6 ± 0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core–shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic configurations in the inner “core” and surface “shell” regions. The atomic structure of these particles is examined by combined X-ray powder diffraction (XRPD), which is sensitive to the crystalline core region of the nanoparticles, and by first shell analysis of extended X-ray absorption fine structure (EXAFS) spectra, which reflects the averaged structure of both the core and the more disordered shell. In the whole temperature range (0–85 °C), XRPD analysis confirms the existence of two well-separated α- and β-hydride phases with the characteristic flat plateau in the phase transition region of the pressure-lattice parameter isotherms. In contrast, first shell in...

Evaluation of soft chemistry methods to synthesize Gd-doped CaMnO3−δ with improved thermoelectric properties

Ceramics of Ca0.96Gd0.04MnO3−δ are prepared via different soft chemistry methods and the solid state route. The phase formation processes of the synthesized powders are compared, and the effects of powder morphology and sintering behavior on the microstructure and thermoelectric properties of the ceramics are investigated.Ceramic powders with particle size of 110nm are obtained from soft chemistry routes. These powders show excellent phase purity and shrink at lower temperatures compared to solid state route powders. Dense ceramics with 1µm mean grain size, homogeneous dopant distribution and good thermoelectric properties are obtained after sintering at 1200°C. Soft chemistry synthesized samples show a figure of merit ZT=0.14 at 700°C. This is higher than the figure of merit of solid state route ceramics, due to a more homogeneous microstructure, better densification and, hence, improved electrical properties. The soft chemistry synthesis methods provide ceramics with comparable thermoelectric performances.

Synthesis, phase formation, and properties of nanomaterials based on the titanium dioxide−iron(III) oxide binary system

The properties of nanomaterials based on the titanium dioxide−iron(III) oxide binary system prepared by low-temperature coprecipitation from aqueous solutions are studied. The effect of thermal treatment conditions and other factors on the process of phase formation and the properties of the synthesized products is examined. It is demonstrated that these materials have a relatively low photocatalytic activity but a high sorption capacity.

Temperature-Induced structural phase transformations in Cu1.50Zn0.30Te and Cu1.75Cd0.05Te single crystals

The results of studying the temperature-induced polymorphic phase transformations in Cu1.50Zn0.30Te and Cu1.75Cd0.05Te single crystals are presented. The single crystals have been investigated in the range of 290–1100 K using X-ray diffraction analysis. The temperature dependences of the unit-cell parameters, X-ray density, and coefficients of thermal expansion for each polymorphic modification of Cu1.50Zn0.30Te and Cu1.75Cd0.05Te single crystals are presented. The influence of cationic substitution (replacement of Cu2+ with Zn2+ and Cd2+ cations) on the phase-formation processes, number of polymorphic modifications, and temperature of structural phase transition in single crystals of these solid solutions is demonstrated.

Influence of alloying the TiC0.5N0.5 carbonitride with zirconium on an interaction mechanism with the Ni–Mo melt

The influence of alloying the TiC0.5N0.5 titanium carbonitride with zirconium on the mechanism and kinetic features of the contact interaction with the Ni–25%Mo melt (t = 1450°C, rarefaction 5 × 10–2 Pa) is investigated for the first time by electron probe microanalysis and scanning electron microscopy. The main effects of the modifying influence of zirconium on the dissolution, phase formation, and structure formation processes which occur during the interaction of the Ti1–n Zr n C0.5N0.5 carbonitride (n = 0.05 and 0.20) with the Ni–Mo melt are revealed and the factors promoting their manifestation are analyzed. The practical absence of zirconium and nitrogen in the composition of the K-phase (the Ti1 – n Mo n C x metastable solid solution, where n ≤ 0.65 and x = 0.7 ± 0.1) is confirmed experimentally. It is shown that the zirconiumenriched Ti0.80Zr0.20C0.5N0.5 carbonitride cannot be recommended as a refractory component of cermet because of the limitations of the chemical character.

Microstructural and magnetic properties of Mn-Fe-P-Si (Fe2 P-type) magnetocaloric compounds

Fe2 P-based magnetocaloric compounds are an important and industrially relevant material class for magnetic refrigeration, yet their microstructure and its influence on the magnetic properties is hardly discussed in literature. We prepared Mn-Fe-P-Si-based samples using a powder metallurgical process and analyzed their microstructural and thermomagnetic properties. XRD, SEM, EDX and EBSD analysis reveal a phosphorous depleted cubic secondary phase in many samples with distinct microstructural properties giving an insight into the phase formation process. A porous morphology was found, hindering the direct application of the materials a magnetocaloric heat exchanger in bulk-like structures. The “virgin” effect could be in-situ observed for the first time on a macroscopic scale using temperature-dependent optical microscopy. Thermomagnetic measurements reveal a difference in transition temperature Tt in comparison to literature values which is attributed to a processing induced deviation from the nominal composition. The isothermal entropy change ΔST and adiabatic temperature change ΔTad were studied as well as their cyclic behavior. The effect of secondary phases is discussed and the importance of the metal/non-metal (M/NM)-ratio is shown. The article presents a road map for the preparation of Mn-Fe-Si-P-based alloys with highest quality.

Thermodynamic-Kinetic Precipitation Modeling. A Case Study: The Amorphous Calcium Carbonate (ACC) Precipitation Pathway Unravelled

Nine accurate experimental data sets on amorphous calcium carbonate (ACC) formation in dilute solution were collected varying temperature and pH. The entire precipitation process is described using a complete thermodynamic-kinetic model. The thermodynamic model includes two new complex chemical interactions whereas the kinetic model is based on the discretized population balance approach. Saturation, primary particles size distribution, average secondary particles size, nucleation, and growth rates, as well as a number of additional parameters on the ACC precipitation reaction, are reported. The excellent agreement among experiments, calculated results, and literature data demonstrates that a complete thermodynamic-kinetic model can significantly contribute toward the understanding of a plausible pathway for precipitating systems. In this case study, the classical nucleation theory, which includes homogeneous nucleation, “true” secondary nucleation, and diffusion limited growth events, is able to completely describe the entire precipitation process. The calculated surface (γ) and cohesion (β) energies range from 28 to 35 and 30 to 42 mJ m–2, respectively, as a function of pH and temperature. Clusters or prenucleation entities act as spectators and are not directly involved in the solid formation pathway. The general methodological approach presented can be readily applied to other solid phase formation processes.

Theoretical and experimental investigation of the nature of crystallization processes in systems Ca(NO3)2—(NH4)2HPO4—Na2SiO3—H2О

The theoretical investigation of phase formation processes in systems Са(NO3)2—(NH4)2НРО4—Na2SiO3—H2О was carried out at the varied concentration of phosphate ions, Si/P molar ratio, and pH taking into account the absorption of CO2 from air. The formation of hydroxyapatite is most probable in aqueous solutions as it was established by the results of calculation of the change in the Gibbs energy of crystallization. The supersaturation of the systems with respect to calcium silicate and calcite and thermodynamic probability of their precipitation together with basic calcium phosphate increase with an increase in the alkalinity of the reaction medium. The formation of mixtures of poorly crystallized nonstoichiometric calcium phosphate and calcium silicate was experimentally detected in the studied media. The method of precipitation from aqueous solutions can be used to produce composites based on these salts for biomedical purposes.

The influence of copper-cobalt co-doping on optical and electrical properties of nanostructures TiO2 thin films prepared by sol-gel

In the following undertaking, we have dealt with both the annealing temperature effects and the co-addition of Cu and Co on the structural, optical, and electrical proprieties of TiO2 thin films elaborated by sol-gel dip-coating route. Thermal analysis of obtained xerogels show that crystallization process of TiO2and CoTiO3 phase formation occur at lower temperature with (Cu-Co) addition. Transmission electron microscopy micrographs reveal that all TiO2 xerogels present agglomerate nature with the decrease of particle sizes when the Co is doped and (Cu-Co) are co-doped TiO2 powders. The crystalline structure and the functional groups of films were estimated by X-ray diffraction, Raman, and fourier transform infrared spectroscopy analyses. Different structure shapes are observed from atomic force microscopy (100 nm) and scanning electron microscope micrographs between films annealed at 800 °C and those annealed at 1000 °C accompanied by an increment in the particle sizes and surface roughness. The optical reflection attains 90% with more undulations, which are presented in the films annealed at 1000 °C than those annealed at 800 °C. The electrical performance at room temperature of both films annealed, respectively, at 800 and 1000 °C exhibit a similar behavior depicting an ohmic nature. The electrical conductivity (σ) of films deduced from I–V testing was found for submitting semi-conducting character with the same factor (σ~10−12) with both films that are annealed, respectively, at 800 and 1000 °C.

Depth-resolved and temperature dependent analysis of phase formation processes in Cu–Zn–Sn–Se films on ZnO substrates

The constitution of secondary phases in kesterite Cu2ZnSnSe4 (CZTSe) thin films is still a limiting factor for their application in solar cells. Therefore an enhanced understanding of phase formation processes during the fabrication of CZTSe films is required. In this study we present a temperature and film-depth dependent phase analysis of Zn/Sn/Cu precursors on ZnO substrates selenized at different temperatures. A special sample preparation step using a focused ion beam was applied to prepare shallow angle cross sections for depth-resolved Raman profiling of the thin films. At low selenization temperatures multiphase structures are demonstrated and a first formation of CZTSe besides secondary phases at only 250 °C is detected. At high selenization temperatures an accumulation of ZnSe at the interface of CZTSe and ZnO substrates is observed. Furthermore indications for the formation of a thin SnO2 interface layer were found by X-ray diffraction, secondary electron microscopy and energy dispersive X-ray spectrometry.